Circuitry designed to sense the current associated with one or more electrical loads are known in the art. As is known, current sensing circuitry can provide for increased control as well as fault diagnosis. For example, U.S. Pat. No. 4,661,717, issued to Nishioka, discloses a load condition determining apparatus capable of detecting normal and abnormal conditions of a load. The apparatus includes a power supply, a drive circuit connected to the power supply and a load circuit, one end of which is connected to the drive circuit. The apparatus also includes a load equivalent circuit connected to the drive circuit, the electrical characteristics of the load equivalent circuit being substantially equal to that of the load circuit. The apparatus further includes a differential amplifier circuit to detect the difference between the input voltages to the differential amplifier circuit in accordance with the conditions of the load circuit and comparing means having first and second comparators connected to the output of the differential amplifier circuit, to determine the normal and abnormal conditions of the load circuit in accordance with the balance and unbalance between the input voltages to the differential amplifier circuit.
U.S. Pat. No. 4,962,350, issued to Fukuda, discloses a load condition detecting and driving system capable of detecting an abnormal condition of the load without being affected by any acceptable variation of the load or change in the voltage supplied by a power source. The system includes switching means having a control terminal, a second terminal of the switching means being coupled to an input terminal of a load, the control terminal being coupled to receive a driving signal for controlling the switching means to apply driving current to the load. The system further includes coupling means coupled between the input terminal and the control terminal for rendering the switching means non-conductive when the load exhibits a short-circuit condition due to a voltage at the output terminal of the load becoming low because of the short-circuit condition.
Other United States patents of lesser relevance include U.S. Pat. No. 3,912,883, issued to Goodyear, U.S. Pat. No. 4,774,510, issued to Steinke, U.S. Pat. No. 4,894,648, issued to Talbot and U.S. Pat. No. 4,931,778, issued to Guajardo.
It is desirable, however, to utilize centralized current sensing of multiple loads wherein single point current sensing identifies normal and abnormal current magnitudes of multiple loads. Such current sensing would have a lower cost than prior art current sensing systems, provide for control, prognostic and diagnostic capabilities while accommodating different numbers and types of loads with appropriate software changes.